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2856 Views 4 Replies Last post: Mar 20, 2013 7:13 AM by MikeHardman RSS
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Mar 18, 2013 5:29 PM

rock ID

Hi all, i thought i would post this rock for id.My first thought was did  it come from space. It looks as though it has melted.At first i thought it was a lump of melted metal.But it turns out it is non magnetic and it will not register on a metal detector.Has anyone got an idea.It is 70 grams.  Thanks.CIMG0004.JPG

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    Mar 18, 2013 9:32 PM (in response to steveb)
    Re: rock ID

    It is probably slag.


    Slag can have quite a range of compositions and structures - from high- to low metal content, frothy to solid, various colours and textures.

    Your one shows smooth flow marks.

    If you go to this page and search on it for 'flow marks', you'll find another example


    It could also be a piece of lava, but it doesn't feel quite right for that.


    The weight on its own doesn't help up. If you calculated its volume (by water displacement), and hence calculated its density, that might narrow the possibilities.


    It might be instructive to break it open, to see the internal structure/texture and colour.




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    • Currently Being Moderated
      Mar 20, 2013 7:13 AM (in response to steveb)
      Re: rock ID


      There appear to be some vesicles. If they were filled with mineral, that would suggest lava; but they are not, hence could be lava or slag.

      Slag has, in many cases, a lot of vesicles. But pieces that show obvious flow/rippling can be almost devoid of them - like this piece. So that is not indicative.

      Both slag and lava can have interiors that are crystalline with this scale of granularity. Also, the colour does not point to one or the other - many lavas are very dark.

      If you were to determine the density, I suspect that, too, would give an ambiguous indication.


      If you know where it came from, and could find more pieces there, some of those might give clues. Knowing the locality could also be useful in itself. Of course, if you could find any of it in an exposure of rock, that would clinch it.


      Looking at a thin section under a petrological microscope would probably resolve the issue. That would enable a determination of the minerals and textures.


      As it is, I can't tell you whether it is slag or solidified lava. Sorry.



      - good collection of types of slag -

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